In the prior art, an ultraviolet (UV) curable ink which is cured by irradiation of ultraviolet rays is used as an ink for an offset sheet-fed printing or an ink-jet printer. To cure the ultraviolet curable ink, an ultraviolet ray irradiation device for irradiating ultraviolet rays is generally used, and regarding the use of printing particularly, since light should be irradiated to an irradiation region elongated in a direction (namely, a width direction of a paper) perpendicular to a transporting direction of a printing paper, a ultraviolet ray irradiation device elongated in a width direction of a paper for irradiating a line-shaped light is used.
As an ultraviolet ray irradiation device, a lamp-type irradiation device using a high-pressure mercury lamp or a mercury xenon lamp as a light source is known, and recently, according to the demands on reduced power consumption, longer life cycle and compact device size, an ultraviolet ray irradiation device using a light emitting diode (LED) as a light source, instead of an existing discharge lamp, has been developed. This ultraviolet ray irradiation device is disclosed in, for example, Patent Literature 1.
The ultraviolet irradiation device (ultraviolet irradiation unit) disclosed in Patent Literature 1 includes a plurality of ultraviolet light emitting semiconductor elements in plural rows, and is installed in a printing device with a posture in which a lengthwise direction of the ultraviolet irradiation unit is in a direction (namely, a width direction) perpendicular to a transporting direction of a printing medium. Since the printing device is configured to print with four-color UV inks of black (K), cyan (C), magenta (M) and yellow (Y), the printing device includes four printing units respectively corresponding to the colors, and four ultraviolet irradiation devices for curing inks, respectively, and these components are disposed along an outer circumference of a drum which transports a printing medium.